Method of improving the coefficient of friction between contacting metal surfaces and article produced thereby



April 9, 1957 LUVI l METHOD OF IMPROVING TH 2,787,965 RICTION BETWEEN URFA C N D A R T I C LE Filed May 2, 1955 United States Patent 9 IVEETHOD F IMPROVING THE COEFFICIENT OF FRICTION BETWEEN CONTACTING METAL SIRFACES AND ARTICLE PRODUCED THERE- B George W. Luvisi, Chicago. 111., assignor to National Aluminate Corporation, Chicago, 11]., a corporation of Delaware Application May 2, 1955, Serial N 0. 505,373

12 Claims. (Cl. 104-1) The present invention relates to a new and improved method for increasing the coeflicient of friction between railway car wheels and rails upon which they operate. More particularly, this invention relates to chemical means for reducing the wheel slippage between locomotive wheels and rails.

The past several decades have produced railway locomotives possessing great power and Weight, thus enabling long, heavily laden trains to be pulled by single engines. With the advent of the extremely heavy locomotive it was felt that driving Wheel slip would be eliminated. It Was soon discovered, however, that the increased static weight carried on the driving wheels did not solve the problem to any great extent. Track sanding techniques were developed but this only partially alleviated the condition. Wheel slippage has proved to be an erractic condition which has not in all cases been satisfactorily explained.

In one explanation of the problem rail slip is said to result from a tough invisible oil film on the wear band of the rail. Traffic and heat destroy this film and high adhesion results. When a light rain occurs or when the rails reach the dew point, as the result of the relatively high humidity, a water vapor film forms across the wear band where it may contact oil deposits on the edge of a rail with the result that a film of oil creeps through and replaces the water film. The oil deposits on the rail sides act as reservoirs for the formation of new oil films and water acts as the transporting agent. The oil deposits on the rail come from journal box oil leakage by way of the outside face and outer portion of the tread of the car wheels. There are other sources of contamination such as road crossings, rail lubricators, and the like.

The importance of solving the problem is strikingly illustrated when it is realized that only 15% of the engines weight can be utilized as tractive force when the rails are greasy and moist, and 30% when the rails are clean, dry and sanded. Even a small improvement in these figures, as expressed in the terms of increased coefficient of friction, would enable railway locomotives to operate more efiiciently and economically as well as providing improved braking for railway locomotives and rolling stock.

It is therefore an object of this invention to provide a method for raising the coeificient of friction between railway car wheels and rails.

Another object is to raise the coeificient of friction between railway car wheels and rails having an oil film thereon.

A further object is to provide a method of decreasing slippage between railway wheels and rails.

Another object is to provide a chemical treatment to prevent locomotive slippage on dry, wet, or oily rails.

Still a further object is to enable railroad locomotives to utilize more of their tractive forces on wet, oily rails than has heretofore been considered possible.

An additional object of the invention is to produce a railway rail containing an adherent coating of a material Patented Apr. 9, 195 7 "ice which substantially prevents slippage between the rail and a locomotive or railway car wheel.

Still a further object of the invention is to provide a rail treating anti-slip composition which is relatively easy to apply and which will remain stable over substantial periods of time.

Another object of the invention is to provide a rail treating anti-slip composition which is stable at temperature below the freezing point of water.

Still another object of the invention is to provide a new and improved method for treating the contacting surfaces of railway car wheels and/or tracks in order to increase the coefficient of friction therebetween. Other objects will appear hereinafter.

In accordance with the invention it has been found that the coefficient of friction between a railway car wheel and tracks may be increased by applying to the contacting surfaces thereof a hydrophilic silica paste.

In the drawing the single figure shows a section of a railway rail containing a coating consisting essentially of a hydrophilic silica paste applied to the bearing surface thereof.

As shown in the drawing, the rail 1 has a bearing surface 2 to which the coating of the hydrophilic silica paste 3 is applied. The coating of the hydrophilic silica paste may also extend over the surface 4 which comes into contact with the wheel fiange of the wheels of locomotives and railway cars.

In accordance with a preferred practice contemplated by the invention the coefiicient of friction between railway car wheels and tracks is increased by applying to at least one of the contacting surfacesthereof a paste of an alcoholated silica sol containing at least 3% silica, as SiOz, by weight, and a hydrophilic aliphatic alcohol.

The preferred pastes employed for the purpose of the invention contain about 3% to about 44% by weight of SiOz and in most cases the compositions employed contain about 12% to about 24% SiOz.

The hydrophilic aliphatic alcohol can be, for example, a low molecular weight aliphatic alcohol such as methanol, ethanol, propanol, isopropanol, butanol and isobutanol, or mixtures thereof. The hydrophilic alcohol can also be a Water soluble ether alcohol such as, for example, the methylether of diethylene glycol or the ethylether of diethylene glycol. It can also be a polyhydric alcohol such as ethylene glycol, diethylene glycol, 1,2-propylene glycol or butylene glycol.

The compositions employed for the purpose of the invention are preferably prepared by adding the alcohol to a silica sol of the desired concentration. Silica sols may be prepared by any number of well known methods, many of which are summarized in Bechtold et al., U. S. 2,574,092, and the present invention contemplates the use of any of such sols. These sols will usually contain at least 3% SiOz and commercial sols are available containing 18% SiOz and 30% SiO2.. For the purpose of the invention the sols used in making the hydrophilic paste preferably contain 30% to 48% SiOz. Silica sols capable of use in the present invention may be conveniently prepared by the ion exchange methods de scribed in Bird, U. S. 2,244,325. They can also be prepared by hydrolyzing sodium silicate with strong mineral cids with the subsequent removal of excess salt.

The Bird patent shows that alkali metal silicate solutions may be contacted with a cation exchange resin in the hydrogen form to produce a silicic acid sol of relatively high purity. After the sol is produced it may be stabilized with a small amount of alkali metal to impart to the finished sol, a high degree of stability. Silica (SiOz) to alkali metal (calculated lasNazo) weight ratios of 50:1 to :1 are preferably employed to impart such stability.

The stabilized sols produced by Birds method are capable of use in the practice of the present invention as produced or they may be concentrated to increase the silica content thereof, several fold. While the Bird patent shows generally the method of concentrating silica sols, there are now several methods available which pro duce sols having a relatively high silica concentration in the form of discrete non-agglomerated particles. Such methods are shown in Bechtold at at, U. S. 2,574,902, Brage et 211., U. S. 2,680,721 and Parma et at, U. S. 2,601,235.

In concentrating colloidal silicic acid sols, the usual methods increase the size of the discrete particles present in the sol. As the general rule the more concentrated the sol, the larger will be the particle size of the silica present. 111121 freshly prepared batch of stabilized 3.5% by weight SiOz sol the particle size is believed to be about 1 to 3 millimicrons in size. If such a sol is concentrated to say about 30% SiOz by using the techniques of Bechtold et 111., U. S. 2,574,902, the average particle size will vary from 15 to 130 mil-limicrons in diameter.

When a water soluble low molecular weight aliphatic alcohol is added to the silica sol, a gelatinous precipitate forms. The resulting alcoholated silica is preferably run through a homogenizer where it is subjected to violent. :agitation in order to produce a uniform homogeneous product. Although the homogenization step is optional, it is very desirable in forming a paste of uniform consistency which is easy to apply to the contacting surfaces of nailway car wheels and tracks.

The amount of alcohol required to form the hydrophilic silica paste can readily be determined by routine experiment. In general, however, the amount should be at least sufficient to produce a gelatinous precipitate of the colloidal silica. The more concentrated the sol, the less will be the amount of alcohol required. This is particularly true when the pH of the sol has been adjusted so that it is slightly acid to neutral, for example, at a pH around 5 to 7. When the sol contains an alkaline material so that the pH is on the alkaline side, it is often necessary to add a larger quantity of alcohol in order to obtain the desired gelatinous precipitate than when the sol is on the acid side.

As can be seen from the previous discussion, a large number or hydrophilic silica pastes are capable of being prepared. The best mode contemplated for the practice of the invention will be illustrated by the following examples describing the preparation of a hydrophilic silica paste and the results obtained by its use in actual field tests.

Example 1' A silica sol having a pH of about 8.3 and containing about 35% Si02 in water was blended with 50% by volume (39.3% by weight) of isopropanol to form a slurry at a temperature of around 70 F. This slurry was divided into 2 portions. One portion was passed through a homogenizer. The second portion was placed in .:a blender and violently agitated. In each instance, the resultant product was a white, easily spreadable material similar in texture to a library paste.

Example I] The composition prepared as in Example l was evaluated in a series of railroad tests. On the day of the tests the weather was clear with the temperature around 55 F. The day before the tests the truck sections used Were given several liberal coatings of journal box oil. The test equipment was a 600 horse power diesel locomotive pulling a baggage car and a modern combine car. On the oiled portion of the rail at full throttle the wheels of the engine spun freely. The composition of Example I was applied to a section of the track with brushes and before the rail dried the engine was run over it. As the spinning wheels contacted the treated surface, the wheel slip was eliminated.

Example III The procedure was the same as in Example II except that the hydrophilic silica paste which had been applied to the rails was allowed to dry. The locomotive was then run over the treated section and again wheel slip was eliminated.

Example IV In another test, the composition of Example I was applied by means of long handled brushes to the wheels of a locomotive spinning on an oiled rail. The locomotive was pulling 16 oars containing scrap metal and two coaches. The application was made several times simultaneously to wheels on the first and third axles of the locomotive. On each application there was a noticeable accelenation of the engine.

Example V A 600 horse power diesel engine pulling 2 coaches was used in this test. The wheels spun freely on the oiled rail. When the composition of Example I was applied to the spinning wheels the train was able to start and stop with no visible sign of wheel slippage during the application of the ianti-slip composition.

Example VI This test was conducted to determine the eflicacy of the composition shown in Example I when applied to the wheels of a locomotive climbing a steep grade. Two diesel engines connected in tandem on a regular freight run pulling a load of 5030 tons were used. The lead engine (1500 horse power) was fitted so that the air pressure, through a tube arrangement, would apply the silica paste to four of the locomotives wheels. As the test began, only one wheel was treated. Even under these conditions the engine suffered less wheel slip than had another similarly laden train operating on the test grade. The amperes, speed and time going up the grade are shown below:

Time in Minutes Ampcres without the use of the alcohol.

As can be seen from this data the engines increased power output was steady without any serious amperage drops which would be indicative of wheel slip. The speed was maintained relatively constant even at the steepest portions of the grade (the last 13 minutes).

While the best mode contemplated for the practice of the invention involves the use of a hydrophilic silica gelatinous paste prepared by adding an aliphatic alcohol to a colloidal silica sol, hydrophilic silica pastes suitable for the practice of the invention can be prepared in other ways For example, suitable hydrophilic silica pastes can be prepared by the addition of caustic soda to silica sols. Suitable hydrophilic silica pastes can also be prepared by precipitating silicic acid from sodium silicates with an acid to form a silica gel. They can also be prepared by mixing a fine silica (e. 51., Dow Corning fine silica) in water to form a sol from which a gelatinous paste can be prepared by precipitation with an electrolyte. The formation of the hydrophilic silica gelatinous paste by gelation of a colloidal silica sol can be conducted by adding to the sol any substance which will cause gelation or cross-linkage of the silica particles present in the sol.

The quantity of the hydrophilic silica paste applied to the conducting surface of either the wheel or rail is subject to some variation but is preferably sufficient to form a thin coating on either the wheel bearing surface, the bearing surface of the rail, or both. As previously indicated, the application can be made directly to the wheel by an applicator which is mounted on the locomotive. The application can also be made directly to the rail. While the quantity applied may vary somewhat, depending upon the silica content of the paste, satisfactory results can be obtained by using at least one gallon of the paste per two-track mile, calculated on the basis of a paste containing around 12% to 24% SiOz.

In a similar manner, other hydrophilic silica pastes can be prepared and utilized in the practice of the invention. The alcoholated silica pastes employed in accordance with the invention have the advantage as compared to aqueous silica sols that they are relatively stable, Whereas the aqueous sols are sometimes unstable toward extraneous electrolytes and conditions in temperature. Furthermore, the pastes employed in the practice of the invention are substantially protected against freezing by the presence of the alcohol which has a lower freezing point than water. Additionally, the invention makes it possible to apply a thin film of colloidal silica to rail surfaces and wheels by the use of simple paste applying devices.

This application is a continuation-in-part of my copending application Serial No. 484,171, filed January 26, 1955, and the disclosure in said parent application is incorporated herein by reference as fully and completely as if it had been set forth in its entirety.

The expression alcoholated silica sol is used herein to describe a hydrophilic silica prepared by adding an ab cohol to a silica sol.

The invention is hereby claimed as follows:

1. The method of improving the coeflicient of friction between contacting metal surfaces capable of moving one with respect to the other which comprises applying to at least one of the contacting surfaces a thin coating of a hydrophilic gelatinous colloidal silica paste, and bringing said metal surfaces into contact with one another with said colloidal silica paste therebetween.

2. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a hydrophilic gelatinous silica paste.

3. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a hydrophilic silica paste consisting essentially of an alcoholated silica sol.

4. The method of improving the coefi'icient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a hydrophilic silica paste consisting essentially of an alcoholated silica sol, said paste containing about 3 to about 44% by weight SiOz.

5. The method of improving the coetficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a hydrophilic silica paste consisting essentially of an alcoholated silica sol, said paste being obtained by adding a hydrophilic aliphatic alcohol to a colloidal silica sol containing at least 30% to 48% by weight SiOz.

6. The method of improving the coeflicient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a hydrophilic silica paste consisting essentially of an alcoholated silica sol, said paste being obtained by adding a water soluble lower aliphatic monohydric alcohol to a silica sol containing 30% to 48% by weight SiOz.

7. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a hydrophilic silica paste consisting essentially of an alcoholated silica sol, said paste being obtained by adding isopropanol to a silica sol containing 30% to 48% by weight SiOz.

8. A railway rail having its wheel bearing surface coated with a hydrophilic gelatinous silica paste.

9. A railway rail having its wheel bearing surface coated with a hydrophilic gelatinous silica paste containing 3% to 44% by weight of SiOz.

10. A railway rail having its wheel bearing surface coated with a hydrophilic silica paste obtained by gelling a colloidal silica sol containing 30% to 48% SiOz with a hydrophilic lower aliphatic alcohol.

11. A railway rail having its wheel bearing surface coated with a hydrophilic silica paste obtained by gelling a colloidal silica sol containing 30% to 48% SiOz with soluble lower aliphatic monohydric alcohol.

12. A railway rail having its wheel bearing surface coated with a hydrophilic silica paste obtained by gelling a colloidal silica sol containing 30% to 48% S102 with isopropanol.

References Cited in the file of this patent UNITED STATES PATENTS 976,543 Bonnton Nov. 22, 1910 1,666,167 Connolly Apr. 17, 1928 2,408,656 Kirk Oct. 1, 1946 

1. THE METHOD OF IMPROVING THE COEFFICIENT OF FRICTION BETWEEN CONTACTING METAL SURFACES CAPABLE OF MOVING ONE WITH RESPECT TO THE OTHER WHICH COMPRISES APPLYING TO AT LEAST ONE OF THE CONTACTING SURFACES A THIN COATING OF A HYDROPHILIC GELATINOUS COLLODIAL SILICA PASTE, AND BRINGING SAID METAL SURFACES INTO CONTACT WITH ONE ANOTHER WITH SAID COLLODIAL SILICA PASTE THEREBETWEEN. 